Rechargeable lithium battery

ABSTRACT

Disclosed is a rechargeable lithium battery including a lithium-aluminum-manganese alloy negative electrode containing lithium as active material, a positive electrode, and a nonaqueous liquid electrolyte containing a solvent, a solute and at least one additive selected from trialkyl phosphite, trialkyl phosphate, trialkyl borate, dialkyl sulfate and dialkyl sulfite.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a rechargeable lithium batterywhich includes a lithium-aluminum-manganese alloy negative electrodecontaining lithium as active material, a positive electrode and anonaqueous liquid electrolyte.

[0003] 2. Description of Related Art

[0004] It is known that when metallic lithium is used for a negativeelectrode of a rechargeable lithium battery, the lithium deposited oncharge tend to grow into dendrites which eventually hinder repetitivecharge-discharge cycling of the battery. This has led to the study touse a lithium-aluminum alloy for a negative electrode of a rechargeablelithium battery. The use of lithium-aluminum alloy appeared to permitrepetitive charge-discharge cycling of the battery since it is capableof electrochemical storage and release of lithium and thus unsusceptibleto dendrite formation.

[0005] The lithium-aluminum alloy, when used for the battery negativeelectrode, is however subjected to subdivision as a result of repetitiveexpansion and shrinkage during charge-discharge cycles. This structuraldestruction results in the failure to obtain satisfactorycharge-discharge cycle performance. In order to prevent such subdivisionof the lithium-aluminum alloy during charge-discharge cycles, JapanesePatent Laying-Open No. Hei 9-320634 proposes the use of alithium-aluminum-manganese alloy. This lithium-aluminum-manganese alloyprovides a satisfactory charge-discharge cycle performance and has beenfound feasible as the negative electrode of rechargeable lithiumbattery.

[0006] However, as technology continues to push up performance andreliability levels of equipments, rechargeable lithium batteries usingsuch a lithium-aluminum-manganese alloy for a negative electrode havecome to show insufficient charge-discharge cycle performancecharacteristics, which has been a problem.

SUMMARY OF THE INVENTION

[0007] The present invention relates to improvement of such arechargeable lithium battery including a lithium-aluminum-manganesealloy negative electrode, and its object is to provide a rechargeablelithium battery which exhibits good charge-discharge performancecharacteristics based on the improved nonaqueous liquid electrolyte.

[0008] In order to attain the above-described object, a rechargeablelithium battery in accordance with the present invention includes alithium-aluminum-manganese negative electrode containing lithium asactive material, a positive electrode and a nonaqueous liquidelectrolyte containing a solute and a solvent. Characteristically, thenonaqueous liquid electrolyte further contains at lease one additiveselected from trialkyl phosphite, trialkyl phosphate, trialkyl borate,dialkyl sulfate and dialkyl sulfite.

[0009] In the present invention, the at lease one additive selected fromtrialkyl phosphite, trialkyl phosphate, trialkyl borate, dialkyl sulfateand dialkyl sulfite may be incorporated in the liquid electrolytesolvent. Such an additive as trialkyl phosphite reacts with thelithium-aluminum-manganese alloy to produce an ionically conductive filmon the lithium-aluminum-manganese alloy. This film inhibits theoccurrence of a side reaction (decomposition reaction of the liquidelectrolyte) between the liquid electrolyte and thelithium-aluminum-manganese alloy during charge-discharge cycles,resulting in obtaining excellent charge-discharge cycle performancecharacteristics.

[0010] In the present invention, the manganese content of thelithium-aluminum-manganese alloy is preferably in the range of 0.1-10weight %, when given by that of an aluminum-manganese alloy into whichlithium is subsequently inserted. If the manganese content falls outsidethe specified range, the ionically conductive film may not be producedin a satisfactory fashion.

[0011] Preferably, the lithium-aluminum-manganese alloy for use in thepresent invention may be in the form of alithium-aluminum-manganese-vanadium orlithium-aluminum-manganese-chromium alloy. The use of such alloyspermits formation of more effective films and thus results in obtainingparticularly good charge-discharge cycle performance characteristics.The vanadium content of the lithium-aluminum-manganese-vanadium alloy ispreferably in the range of 0.01-5 weight %, when given by that of analuminum-manganese-vanadium alloy into which the lithium is subsequentlyinserted. The chromium content of thelithium-aluminum-manganese-chromium alloy is preferably in the range of0.01-3 weight %, when given by that of an aluminum-manganese-chromiumalloy into which lithium is subsequently inserted.

[0012] In the present invention, the additive is preferably incorporatedin the amount of 0.1-20%, based on the total volume of the solvent andthe additive. If its amount is below 0.1% by volume, the ionicallyconductive film may not be produced in a satisfactory fashion. On theother hand, if its amount exceeds 20% by volume, the film may be formedexcessively thick to hinder the charge-discharge process. Accordingly,particularly good charge-discharge cycle performance characteristics areobtained when the amount by volume of the additive is 0.1-20% of thetotal volume of the solvent and the additive.

[0013] In the present invention, the positive electrode may be composedof any positive electrode material generally known to be useful forrechargeable lithium batteries. Examples of positive electrode materialsinclude manganese dioxide, vanadium pentoxide, niobium oxide, lithiumcobalt oxide, lithium nickel oxide, spinel manganese and the like. Theimproved charge-discharge cycle performance characteristics are obtainedwhen a lithium-manganese complex oxide is used for the positiveelectrode material. Further improved charge-discharge cycle performancecharacteristics result when the lithium-manganese complex oxide is acomplex oxide of lithium and manganese into which boron or boroncompound is incorporated in the form of solid solution.

[0014] The lithium-manganese complex oxide containing boron or a boroncompound in the form of solid solution is disclosed, for example, inJapanese Patent Laying-Open No. Hei 8-2769366 (1996). Specifically, aratio of number of boron to manganese atoms (B/Mn) is 0.01-0.20. A meanvalence number of manganese is at least 3.80. This complex oxide can beprepared by a method wherein a mixture of a boron, lithium and manganesecompound, in a ratio of numbers of atoms (B:Li:Mn) of0.01-0.20:0.1-2.0:1, is heat treated at a temperature of 150-430° C.,preferably of 250-430° C., more preferably of 300-430° C. If thetemperature of heat treatment is below 150° C., several problems ariseincluding insufficient progress of reaction and insufficient moistureremoval from MnO₂. On the other hand, if the heat treatment temperatureexceeds 430° C., decomposition of MnO₂ may be caused to occur to reducea mean valence number of manganese to less than 3.80. As a result, theboron-containing lithium-manganese complex oxide during charge undergoesa change in electronic state to become unstable, resulting in theincreased tendency to decompose and dissolve in the nonaqueous liquidelectrolyte. The heat treatment is preferably performed in the air.

[0015] Examples of boron compounds include boron oxide (B₂O₃), boricacid (H₃BO₃), metaboric acid (HBO₂), lithium metaborate (LiBO₂) andlithium tetraborate (Li₂B₄O₇). Examples of lithium compounds includelithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), lithium oxide(Li₂O) and lithium nitrate (LiNO₃). Examples of manganese compoundsinclude manganese dioxide and manganese oxyhydroxide (MnOOH).

[0016] Examples of nonaqueous liquid electrolyte solutes found effectiveto give good charge-discharge cycle performances include lithiumtrifluoromethane sulfonimide, lithium pentafluoroethane sulfonimide andlithium trifluoromethane sulfonmethide, which will be later illustratedin the Examples.

[0017] Examples of nonaqueous liquid electrolyte solvents foundeffective to provide good charge-discharge cycle performances are mixedsolvents containing at least one organic solvent selected from the groupconsisting of ethylene carbonate, propylene carbonate, butylenecarbonate, vinylene carbonate, γ-butyrolactone and sulfolane, and alsocontaining at least one organic solvent selected from the groupconsisting of 1,2-dimethoxyethane, 1,2-diethoxyethane,1,2-ethoxymethoxyethane, tetrahydrofuran, 1,3-dioxolane, dimethylcarbonate, diethyl carbonate and methyl ethyl carbonate. The liquidelectolytes containing such mixed solvents exhibit high ionicconductivity. When such mixed solvents are used in the preparation ofthe liquid electrolyte, a film having good ionic conductivity is formedon the negative electrode, resulting in the improved charge-dischargecycle performance characteristics.

[0018] The present invention utilizes a lithium-aluminum-manganese alloyfor the negative electrode and the above-specified additive forincorporation in the liquid electrolyte. This prevents occurrence of adecomposition reaction of the liquid electrolyte on the negativeelectrode during charge, resulting in obtaining good charge-dischargecycle performance characteristics.

BRIEF DESCRIPTION OF THE DRAWING

[0019]FIG. 1 is a schematic sectional view of a flat-disc typerechargeable lithium battery in accordance with one embodiment of thepresent invention.

DESCRIPTION OF PREFERRED EXAMPLES

[0020] The present invention is now described in more detail withreference to preferred examples. It will be recognized that thefollowing examples merely illustrate the practice of the presentinvention but are not intended to be limiting thereof. Suitable changesand modifications can be effected without departing from the scope ofthe present invention.

EXAMPLE 1-1

[0021] (A) Positive Electrode Preparation

[0022] Lithium hydroxide (LiOH), boron oxide (B₂O₃) and manganesedioxide (MnO₂) were mixed such that a ratio of numbers of Li, B and Mnatoms (Li:B:Mn) was brought to 0.53:0.06:1.00. The mixture was heattreated (calcined) at 375° C. for a period of 20 hours and then crushedto obtain a boron-containing lithium-manganese complex oxide for use aspositive electrode active material. The obtained boron-containinglithium-manganese complex oxide was subjected to X-ray diffractionanalysis. Only two peaks, i.e., a peak of Li₂MnO₃ and another peak ofMnO₂ shifted slightly toward a lower angle side from a normal position,were observed in the X-ray diffraction pattern. Also, a mean valencenumber of manganese in the boron-containing lithium-manganese complexoxide was determined to be 3.80.

[0023] The following procedure was utilized to determine a mean valencenumber of manganese in the boron-containing lithium-manganese complexoxide. First, a sample was allowed to dissolve in hydrochloric acid toprepare a solution. Then, an aqueous solution of ammonium ferroussulfate was added to the solution. An effective amount of oxygen presentin the solution (oxidizing ability of manganese) was determined by achemical titration method wherein excess ammonium ferrous sulfate wastitrated with an aqueous solution of potassium permanganate. An amountof manganese present in the solution was also determined by atomicabsorption spectrometry. The mean valence number of manganese in theboron-containing lithium-manganese complex oxide was calculated from thedetermined effective oxygen amount and manganese amount.

[0024] The mean valence number of manganese was found to be smaller thana normal manganese stoichiometry of 4. This is considered due to theentrance of a slight amount of lithium into a solid solution of MnO₂,which is considered also responsible for the shifting of the MnO₂ peaktoward a lower angle side in the X-ray diffraction pattern.

[0025] The boron-containing lithium-manganese complex oxide (in thepowder form), carbon black (in the powder form) as an electronicconductor and a fluoro resin (in the powder form) as a binder wereblended in the weight ratio of 85:10:5 to prepare a cathode mix. Thiscathode mix was formed in a mold into a circular disc and then driedunder reduced pressure at 250° C. for a period of 2 hours to prepare apositive electrode.

[0026] (B) Negative Electrode Preparation

[0027] Lithium was electrochemically inserted in an aluminum-manganesealloy (Al—Mn alloy) containing 1 weight % of manganese to prepare alithium-aluminum-manganese alloy (Li—Al—Mn alloy) which was subsequentlypunched to remove therefrom a circular-disc to prepare a negativeelectrode.

[0028] (C) Nonaqueous Liquid Electrolyte Preparation

[0029] Propylene carbonate (PC) and 1,2-dimethoxyethane (DME), as amixed solvent, and trimethyl phosphite as an additive were blended inthe ratio by volume of 47.5:47.5:5 to obtain a mixture. Then, lithiumtrifluoromethane sulfonimide (LiN(CF₃SO₂)₂) as a solute was allowed todissolve in the mixed solvent to a concentration of 1 mole/liter toprepare a nonaqueous liquid electrolyte.

[0030] (D) Battery Assembly

[0031] Using the above-prepared positive electrode, negative electrodeand nonaqueous liquid electrolyte, a flat-disc type battery A-1(rechargeable lithium battery sized 24 mm in outer diameter and 3 mm inthickness) according to the present invention was assembled. Theseparator used was a microporous polypropylene membrane into which thenonaqueous liquid electrolyte was impregnated.

[0032]FIG. 1 is a schematic sectional view of the assembled battery A-1in accordance with the present invention. The shown battery A-1 of thepresent invention includes a negative electrode 1, a positive electrode2, a separator 3 for separating these electrodes 1 and 2 from eachother, a negative can 4, a positive can 5, a negative current collector6 made of a stainless steel (SUS 304) sheet, a positive currentcollector 7 made of a stainless steel (SUS 316) sheet and an insulatinggasket 8 made of polypropylene. The discharge capacity of 90-100 mAh wasreported for all the batteries assembled in the following Examples andComparative Examples.

[0033] The negative and positive electrodes 1 and 2 are located onopposite sides of the separator 3 impregnated with the nonaqueous liquidelectrolyte and the assembly is housed in a battery casing defined bythe negative and positive cans 4 and 5. The negative current collector 6connects the negative electrode 1 to the negative can 4. The positivecurrent collector 7 connects the positive electrode 2 to the positivecan 5. A chemical energy produced in the battery can be delivered in theform of an electrical energy from terminals connected to the negativeand positive cans 4 and 5.

[0034] The internal resistance of the battery prior to being subjectedto charge-discharge cycle was measured to be about 10 Ω. Likewise, theinternal resistance of about 10 Ω was reported for all the batteries inthe following Examples and Comparative Examples.

EXAMPLE 1-2

[0035] The procedure of Example 1-1 was followed, except that theadditive was changed from trimethyl phosphite to trimethyl phosphate inthe preparation of the nonaqueous liquid electrolyte, to assemble abattery A-2 in accordance with the present invention.

EXAMPLE 1-3

[0036] The procedure of Example 1-1 was followed, except that theadditive was changed from trimethyl phosphite to trimethyl borate in thepreparation of the nonaqueous liquid electrolyte, to assemble a batteryA-3 in accordance with the present invention.

EXAMPLE 1-4

[0037] The procedure of Example 1-1 was followed, except that theadditive was changed from trimethyl phosphite to dimethyl sulfate in thepreparation of the nonaqueous liquid electrolyte, to assemble a batteryA-4 in accordance with the present invention.

EXAMPLE 1-5

[0038] The procedure of Example 1-1 was followed, except that theadditive was changed from trimethyl phosphite to dimethyl sulfite in thepreparation of the nonaqueous liquid electrolyte, to assemble a batteryA-5 in accordance with the present invention.

COMPARATIVE EXAMPLE 1-1

[0039] The procedure of Example 1-1 was followed, except that theadditive was excluded in the preparation of the nonaqueous liquidelectrolyte, to assemble a comparative battery X-1.

CHARGE-DISCHARGE CYCLE TEST

[0040] Each of the batteries A-1-A-5 in accordance with the presentinvention and the comparative battery X-1 was subjected to repetitivecharge-discharge cycling under the conditions of a charge-discharge rateof 10 mA, end-of-charge voltage of 3.2 V and end-of-discharge voltage of2.0 V to measure the number of cycles during which the dischargecapacity dropped to a half of its initial value. The number of cycles asmeasured is shown in Table 1. TABLE 1 Number Designation SolventAdditive Solute of of Battery (Volume Ratio) (Volume Ratio) (1M) CyclesA1 PC/DME Trimethyl LiN(CF₃SO₂)₂ 65 (47.5/47.5) Phosphite(5) A2 PC/DMETrimethyl LiN(CF₃SO₂)₂ 64 (47.5/47.5) Phosphate(5) A3 PC/DME TrimethylLiN(CF₃SO₂)₂ 63 (47.5/47.5) Borate(5) A4 PC/DME Dimethyl LiN(CF₃SO₂)₂ 61(47.5/47.5) Sulfate(5) A5 PC/DME Dimethyl LiN(CF₃SO₂)₂ 60 (47.5/47.5)Sulfite(5) X1 PC/DME Absent LiN(CF₃SO₂)₂ 25 (50/50)

[0041] As can be seen from Table 1, the cycle number of less than 30 wasreported for the comparative battery X-1 which excluded the additive (atleast one of trialkyl phosphite, trialkyl phosphate, trialkyl borate,dialkyl sulfate and dialkyl sulfite) from the nonaqueous liquidelectrolyte. By contrast, the increased cycle numbers were reported forthe batteries A-1-A-5 of the present invention incorporating at leastone of trialkyl phosphite, trialkyl phosphate, trialkyl borate, dialkylsulfate and dialkyl sulfite in the nonaqueous liquid electrolyte. Theimprovement in charge-discharge cycle performance characteristics isconsidered due to the reaction between the lithium-aluminum-manganesealloy and at least one of trialkyl phosphite, trialkyl phosphate,trialkyl borate, dialkyl sulfate and dialkyl sulfite, which produces onthe lithium-aluminum-manganese alloy an ionically conductive filmeffective to prevent the occurrence of a side reaction between theliquid electrolyte and the lithium-aluminum-manganese alloy duringcharge-discharge cycles.

EXAMPLE 2-1

[0042] In the negative electrode preparation, lithium waselectrochemically inserted in an aluminum-manganese alloy (Al—Mn alloy)containing 0.1 weight % of manganese to prepare thelithium-aluminum-manganese alloy (Li—Al—Mn alloy). Otherwise, theprocedure of Example 1-1 was followed to assemble a battery B-1 inaccordance with the present invention.

EXAMPLE 2-2

[0043] In the negative electrode preparation, lithium waselectrochemically inserted into an aluminum-manganese alloy (Al—Mnalloy) containing 0.5 weight % of manganese to prepare thelithium-aluminum-manganese alloy (Li—Al—Mn alloy). Otherwise, theprecedure of Example 1-1 was followed to assemble a battery B-2 inaccordance with the present invention.

EXAMPLE 2-3

[0044] In the negative elctrode preparation, lithium waselectrochemically inserted into an aluminum-manganese alloy (Al—Mnalloy) containing 1 weight % of manganese to prepare thelithium-aluminum-manganese alloy (Li—Al—Mn alloy). That is, theprocedure of Example 1-1 was exactly followed to assemble a battery B-3(identical to the battery A-1) in accordance with the present invention.

EXAMPLE 2-4

[0045] In the negative electrode preparation, lithium waselectrochemically inserted in an aluminum-manganese alloy (Al—Mn alloy)containing 5 weight % of manganese to prepare thelithium-aluminum-manganese alloy (Li—Al—Mn alloy). Otherwise, theprocedure of Example 1-1 was followed to assemble a battery B-4 inaccordance with the present invention.

EXAMPLE 2-5

[0046] In the negative electrode preparation, lithium waselectrochemically inserted in an aluminum-manganese alloy (Al—Mn alloy)containing 10 weight % of manganese to prepare thelithium-aluminum-manganese alloy (Li—Al—Mn alloy). Otherwise, theprocedure of Example 1-1 was followed to assemble a battery B-5 inaccordance with the present invention.

CHARGE-DISCHARGE CYCLE TEST

[0047] Each of the batteries B-1-B-5 in accordance with the presentinvention was subjected to a charge-discharge cycle test under the sameconditions as in the preceding test. The results are given in thefollowing Table 2. TABLE 2 Designation Mn Content (wt %) Number of ofBattery in Al—Mn Alloy Cycles B1 0.1 60 B2 0.5 62 B3 (A1) 1 65 B4 5 64B5 10  62

[0048] As can be seen from Table 2, good charge-discharge cycleperformance characteristics are obtained for the batteries B-1-B-5 ofthe present invention which include negative electrodes prepared usingaluminum-manganese alloys containing 0.1-10 weight % of manganese.

EXAMPLE 3-1

[0049] Lithium was electrochemically inserted in analuminum-manganese-vanadium alloy (Al—Mn—V alloy) containing 1 weight %of manganese and 0.1 weight % of vanadium to prepare alithium-aluminum-manganese-vanadium alloy (Li—Al—Mn—V alloy) negativeelectrode. The procedure of Example 1-1 was followed, except that theabove prepared negative electrode was used, to assemble a battery C-1 inaccordance with the present invention.

EXAMPLE 3-2

[0050] Lithium was electrochemically inserted in analuminum-manganese-chromium alloy (Al—Mn—Cr alloy) containing 1 weight %of manganese and 0.1 weight % of chromium to prepare alithium-aluminum-manganese-chromium alloy (Li—Al—Mn—Cr alloy) negativeelectrode. The procedure of Example 1-1 was followed, except that theabove prepared negative electrode was used, to assemble a battery C-2 inaccordance with the present invention.

CHARGE-DISCHARGE CYCLE TEST

[0051] Each of the batteries C-1 and C-2 in accordance with the presentinvention was subjected to a charge-discharge cycle test under the sameconditions as in the preceding test. The results are given in thefollowing Table 3. TABLE 3 Designation Alloy Number of of Battery (wt %)Cycles C1 Al—Mn—V (Al: 98.9, Mn: 1, V: 0.1) 69 C2 Al—Mn—Cr (Al: 98.9,Mn: 1, Cr: 0.1) 67 A1 Al—Mn (Al: 99, Mn: 1) 65

[0052] As can be seen from Table 3, further improved charge-dischargecycle performance characteristics are obtained when thelithium-aluminum-manganese alloy was replaced by thelithium-aluminum-manganese-vanadium orlithium-aluminum-manganese-chromium alloy, which is considered due tothe formation of improved films.

EXAMPLE 4-1

[0053] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 0.1% by volume, based on the totalvolume of the solvent and trimethyl phosphite. Otherwise, the procedureof Example 1-1 was followed to assemble a battery D-1 in accordance withthe present invention.

EXAMPLE 4-2

[0054] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 0.5% by volume, based on the totalvolume of the solvent and trimethyl phosphite. Otherwise, the procedureof Example 1-1 was followed to assemble a battery D-2 in accordance withthe present invention.

EXAMPLE 4-3

[0055] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 1% by volume, based on the totalvolume of the solvent and trimethyl phosphite. Otherwise, the procedureof Example 1-1 was followed to assemble a battery D-3 in accordance withthe present invention.

EXAMPLE 4-4

[0056] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 5% by volume, based on the totalvolume of the solvent and trimethyl phosphite. That is, the procedure ofExample 1-1 was exactly followed to assemble a battery D-4 (identical tothe battery A-1) in accordance with the present invention.

EXAMPLE 4-5

[0057] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 10% by volume, based on the totalvolume of the solvent and trimethyl phosphite. Otherwise, the procedureof Example 1-1 was followed to assemble a battery D-5 in accordance withthe present invention.

EXAMPLE 4-6

[0058] Trimethyl phosphite, as the additive, was loaded in the liquidelectrolyte solvent in the amount of 20% by volume, based on the totalvolume of the solvent and trimethyl phosphite. Otherwise, the procedureof Example 1-1 was followed to assemble a battery D-6 in accordance withthe present invention.

CHARGE-DISCHARGE CYCLE TEST

[0059] Each of the batteries D-1 and D-6 in accordance with the presentinvention was subjected to a charge-discharge cycle test under the sameconditions as in the preceding test. The results are given in thefollowing Table 4. TABLE 4 Number Designation Solvent Additive Solute ofof Battery (Volume Ratio) (Volume Ratio) (1M) Cycles D1 PC/DME TrimethylLiN(CF₃SO₂)₂ 50 (49.95/49.95) Phosphite(0.1) D2 PC/DME TrimethylLiN(CF₃SO₂)₂ 55 (49.75/49.75) Phosphite(0.5) D3 PC/DME TrimethylLiN(CF₃SO₂)₂ 60 (49.5/49.5) Phosphite(1) D4 (A1) PC/DME TrimethylLiN(CF₃SO₂)₂ 65 (47.5/47.5) Phosphite(5) D5 PC/DME TrimethylLiN(CF₃SO₂)₂ 62 (45/45) Phosphite(10) D6 PC/DME Trimethyl LiN(CF₃SO₂)₂60 (40/40) Phosphite(20)

[0060] As can be seen from Table 4, improved charge-discharge cycleperformance characteristics are obtained for the batteries D-1 and D-6of the present invention which include the nonaquous liquid electrolytecontaining the specific additive in the amount by volume of 0.1-20%,based on the total volume of the electrolyte solvent and the additive.

EXAMPLE 5-1

[0061] Lithium trifluoromethane sulfonimide (LiN(CF₃SO₂)₂) was used asthe nonaqueous liquid electrolyte solute. That is, the procedure ofExample 1-1 was exactly followed to assemble a battery E-1 (identical tothe battery A-1)

EXAMPLE 5-2

[0062] The procedure of Example 1-1 was followed, except that lithiumpentafluoroethane sulfonimide (LiN(C₂F₅SO₂)₂) was used as the nonaqueousliquid electrolyte solute, to assemble a battery E-2 in accordance withthe present invention.

EXAMPLE 5-3

[0063] The procedure of Example 1-1 was followed, except that lithiumtrifluoromethane sulfonmethide (LiC(CF₃SO₂)₃) was used as the nonaqueousliquid electrolyte solute, to assemble a battery E-3 in accordance withthe present invention.

EXAMPLE 5-4

[0064] The procedure of Example 1-1 was followed, except that lithiumtrifluoromethanesulfonate (LiCF₃SO₃) was used as the nonaqueous liquidelectrolyte solute, to assemble a battery E-4 in accordance with thepresent invention.

EXAMPLE 5-5

[0065] The procedure of Example 1-1 was followed, except that lithiumhexafluorophosphate (LiPF₆) was used as the nonaqueous liquidelectrolyte solute, to assemble a battery E-5 in accordance with thepresent invention.

EXAMPLE 5-6

[0066] The procedure of Example 1-1 was followed, except that lithiumtetrafluoroborate (LiBF₄) was used as the nonaqueous liquid electrolytesolute, to assemble a battery E-6 in accordance with the presentinvention.

EXAMPLE 5-7

[0067] The procedure of Example 1-1 was followed, except that lithiumhexafluoroarsenate (LiAsF₆) was used as the nonaqueous liquidelectrolyte solute, to assemble a battery E-7 in accordance with thepresent invention.

EXAMPLE 5-8

[0068] The procedure of Example 1-1 was followed, except that lithiumperchlorate (LiClO₄) was used as the nonaqueous liquid electrolytesolute, to assemble a battery E-8 in accordance with the presentinvention.

CHARGE-DISCHARGE CYCLE TEST

[0069] Each of the batteries E-1-E-8 in accordance with the presentinvention was subjected to a charge-discharge cycle test under the sameconditions as in the preceding test. The results are given in thefollowing Table 5. TABLE 5 Number Designation Solvent Additive Solute ofof Battery (Volume Ratio) (Volume Ratio) (1M) Cycles E1 (A1) PC/DMETrimethyl LiN(CF₃SO₂)₂ 50 (47.5/47.5) Phosphite(5) E2 PC/DME TrimethylLiN(C₂F₅SO₂)₂ 64 (47.5/47.5) Phosphite(5) E3 PC/DME TrimethylLiC(CF₃SO₂)₃ 63 (47.5/47.5) Phosphite(5) E4 PC/DME Trimethyl LiCF₃SO₃ 56(47.5/47.5) Phosphite(5) E5 PC/DME Trimethyl LiPF₆ 52 (47.5/47.5)Phosphite(5) E6 PC/DME Trimethyl LIBF₄ 54 (47.5/47.5) Phosphite(5) E7PC/DME Trimethyl LiAsF₆ 53 (47.5/47.5) Phosphite(5) E8 PC/DME TrimethylLiClO₄ 44 (47.5/47.5) Phosphite(5)

[0070] As can be seen from Table 5, the cycle frequencies of less than60 were reported for the batteries E-4-E-8 using LiCF₃SO₃, LiPF₆, LiBF₄,LiAsF₆ and LiClO₄ for their respective liquid electrolyte solutes. Bycontrast, the increased cycle frequencies were reported for thebatteries E-1-E-3 using LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ and LiC(CF₃SO₂)₃ fortheir respective liquid electrolyte solutes. This effect of improvingcharge-discharge cycle performance characteristics is found to becomesignificant particularly when LiN(CF₃SO₂)₂ is used for the liquidelectrolyte solute.

EXAMPLE 6-1

[0071] Ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-1 inaccordance with the present invention.

EXAMPLE 6-2

[0072] Butylene carbonate (BC) and 1,2-dimethoxyethane (DME) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-2 inaccordance with the present invention.

EXAMPLE 6-3

[0073] Vinylene carbonate (VC) and 1,2-dimethoxyethane (DME) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-3 inaccordance with the present invention.

EXAMPLE 6-4

[0074] γ-butyrolactone (γ-BL) and 1,2-dimethoxyethane (DME) were blendedin the ratio by volume of 47.5:47.5 to prepare a mixed solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-4 in accordance withthe present invention.

EXAMPLE 6-5

[0075] Sulfolane (SL) and 1,2-dimethoxyethane (DME) were blended in theratio by volume of 47.5:47.5 to prepare a mixed solvent for inclusion inthe nonaqueous liquid electrolyte. Otherwise, the procedure of Example1-1 was followed to assemble a battery F-5 in accordance with thepresent invention.

EXAMPLE 6-6

[0076] Propylene carbonate (PC) and 1,2-diethoxyethane (DEE) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-6 inaccordance with the present invention.

EXAMPLE 6-7

[0077] Propylene carbonate (PC) and 1,2-ethoxymethoxyethane (EME) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-7 inaccordance with the present invention.

EXAMPLE 6-8

[0078] Propylene carbonate (PC) and tetrahydrofuran (THF) were blendedin the ratio by volume of 47.5:47.5 to prepare a mixed solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-8 in accordance withthe present invention.

EXAMPLE 6-9

[0079] Propylene carbonate (PC) and 1,3-dioxolane (DOXL) were blended inthe ratio by volume of 47.5:47.5 to prepare a mixed solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-9 in accordance withthe present invention.

EXAMPLE 6-10

[0080] Propylene carbonate (PC) and dimethyl carbonate (DMC) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-10 inaccordance with the present invention.

EXAMPLE 6-11

[0081] Propylene carbonate (PC) and diethyl carbonate (DEC) were blendedin the ratio by volume of 47.5:47.5 to prepare a mixed solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-11 in accordancewith the present invention.

EXAMPLE 6-12

[0082] Propylene carbonate (PC) and ethyl methyl carbonate (EMC) wereblended in the ratio by volume of 47.5:47.5 to prepare a mixed solventfor inclusion in the nonaqueous liquid electrolyte. Otherwise, theprocedure of Example 1-1 was followed to assemble a battery F-12 inaccordance with the present invention.

EXAMPLE 6-13

[0083] Propylene carbonate (PC) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-13 in accordance withthe present invention.

EXAMPLE 6-14

[0084] Ethylene carbonate (EC) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-14 in accordance withthe present invention.

EXAMPLE 6-15

[0085] Butylene carbonate (BC) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-15 in accordance withthe present invention.

EXAMPLE 6-16

[0086] Vinylene carbonate (VC) was used as a sole solvent for incolusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-16 in accordance withthe present invention.

EXAMPLE 6-17

[0087] γ-butyrolactone (γ-BL) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-17 in accordance withthe present invention.

EXAMPLE 6-18

[0088] Sulfolane (SL) was used as a sole solvent for inclusion in thenonaqueous liquid electrolyte. Otherwise, the procedure of Example 1-1was followed to assemble a battery F-18 in accordance with the presentinvention.

EXAMPLE 6-19

[0089] 1,2-dimethoxyethane (DME) was used as a sole solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-19 in accordancewith the present invention.

EXAMPLE 6-20

[0090] 1,2-diethoxyethane (DEE) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-20 in accordance withthe present invention.

EXAMPLE 6-21

[0091] 1,2-ethoxymethoxyethane (EME) was used as a sole solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-21 in accordancewith the present invention.

EXAMPLE 6-22

[0092] Tetrahydrofuran (THF) was used as a sole solvent for inclusion inthe nonaqueous liquid electrolyte. Otherwise, the procedure of Example1-1 was followed to assemble a battery F-22 in accordance with thepresent invention.

EXAMPLE 6-23

[0093] 1,3-dioxolane (DOXL) was used as a sole solvent for inclusion inthe nonaqueous liquid electrolyte. Otherwise, the procedure of Example1-1 was followed to assemble a battery F-23 in accordance with thepresent invention.

EXAMPLE 6-24

[0094] Dimethyl carbonate (DMC) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-24 in accordance withthe present invention.

EXAMPLE 6-25

[0095] Diethyl carbonate (DEC) was used as a sole solvent for inclusionin the nonaqueous liquid electrolyte. Otherwise, the procedure ofExample 1-1 was followed to assemble a battery F-25 in accordance withthe present invention.

EXAMPLE 6-26

[0096] Ethyl methyl carbonate (EMC) was used as a sole solvent forinclusion in the nonaqueous liquid electrolyte. Otherwise, the procedureof Example 1-1 was followed to assemble a battery F-26 in accordancewith the present invention.

CHARGE-DISCHARGE CYCLE TEST

[0097] Each of the batteries A-1 and E-1-E-26 in accordance with thepresent invention was subjected to a charge-discharge cycle test underthe same conditions as in the preceding test. The results are given inthe following Table 6. TABLE 6 Number Designation Solvent AdditiveSolute of of Battery (Volume Ratio) (Volume Ratio) (1M) Cycles A1 PC/DMETrimethyl LiN(CF₃SO₂)₂ 65 (47.5/47.5) Phosphite(5) F1 EC/DME TrimethylLiN(CF₃SO₂)₂ 66 (47.5/47.5) Phosphite(5) F2 BC/DME TrimethylLiN(CF₃SO₂)₂ 63 (47.5/47.5) Phosphite(5) F3 VC/DME TrimethylLiN(CF₃SO₂)₂ 55 (47.5/47.5) Phosphite(5) F4 γ-BL/DME TrimethylLiN(CF₃SO₂)₂ 55 (47.5/47.5) Phosphite(5) F5 SL/DME TrimethylLiN(CF₃SO₂)₂ 57 (47.5/47.5) Phosphite(5) F6 PC/DEE TrimethylLiN(CF₃SO₂)₂ 58 (47.5/47.5) Phosphite(5) F7 PC/EME TrimethylLiN(CF₃SO₂)₂ 54 (47.5/47.5) Phosphite(5) F8 PC/THF TrimethylLiN(CF₃SO₂)₂ 52 (47.5/47.5) Phosphite(5) F9 PC/DOXL TrimethylLiN(CF₃SO₂)₂ 53 (47.5/47.5) Phosphite(5) F10 PC/DMC TrimethylLiN(CF₃SO₂)₂ 51 (47.5/47.5) Phosphite(5) F11 PC/DEC TrimethylLiN(CF₃SO₂)₂ 51 (47.5/47.5) Phosphite(5) F12 PC/EMC TrimethylLiN(CF₃SO₂)₂ 50 (47.5/47.5) Phosphite(5) F13 PC(95) TrimethylLiN(CF₃SO₂)₂ 46 Phosphite(5) F14 EC(95) Trimethyl LiN(CF₃SO₂)₂ 49Phosphite(5) F15 BC(95) Trimethyl LiN(CF₃SO₂)₂ 44 Phosphite(5) F16VC(95) Trimethyl LiN(CF₃SO₂)₂ 45 Phosphite(5) F17 γ-BL(95) TrimethylLiN(CF₃SO₂)₂ 43 Phosphite(5) F18 SL(95) Trimethyl LiN(CF₃SO₂)₂ 44Phosphite(5) F19 DME(95) Trimethyl LiN(CF₃SO₂)₂ 41 Phosphite(5) F20DEE(95) Trimethyl LiN(CF₃SO₂)₂ 45 Phosphite(5) F21 EME(95) TrimethylLiN(CF₃SO₂)₂ 47 Phosphite(5) F22 THF(95) Trimethyl LiN(CF₃SO₂)₂ 46Phosphite(5) F23 DOXL(95) Trimethyl LiN(CF₃SO₂)₂ 47 Phosphite(5) F24DMC(95) Trimethyl LiN(CF₃SO₂)₂ 41 Phosphite(5) F25 DEC(95) TrimethylLiN(CF₃SO₂)₂ 48 Phosphite(5) F26 EMC(95) Trimethyl LiN(CF₃SO₂)₂ 41Phosphite(5)

[0098] As can be seen from Table 6, cycle frequencies of less than 50were reporeted for the batteries F-13-F-26 using sole solvents forincorporation in their respective nonaqueous liquid electrolytes. Bycontrast, particularly good charge-discharge cycle performancecharacteristics were reported for the batteries A-1 and F-1-F-12 usingany of mixed solvents containing at least one organic solvent selectedfrom the group consisting of ethylene carbonate, propylene carbonate,butylene carbonate, vinylene carbonate, γ-butyrolactone and sulfolane,and also at least one organic solvent selected from the group consistingof 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-ethoxymethoxyethane,tetrahydrofuran, 1,3-dioxolane, dimethyl carbonate, diethyl carbonateand methyl ethyl carbonate for inclusion in their respective nonaqueousliquid electrolytes.

[0099] In accordance with the present invention, rechargeable lithiumbatteries can be provided which exhibit good charge-discharge cycleperformance characteristics with extremely high reliability.

What is claimed is:
 1. A rechargeable lithium battery including: alithium-aluminum-manganese alloy negative electrode containing lithiumas active material; a positive electrode; and a nonaqueous liquidelectrolyte containing a solvent, a solute and at least one additiveselected from trialkyl phosphite, trialkyl phosphate, trialkyl borate,dialkyl sulfate and dialkyl sulfite.
 2. The rechargeable lithium batteryof claim 1 , wherein the manganese content of saidlithium-aluminum-manganese alloy is in the range of 0.1-10 weight %,when given by that of an aluminum-manganese alloy into which the lithiumis subsequently inserted.
 3. The rechargeable lithium battery of claim 1, wherein said lithium-aluminum-manganese alloy is alithium-aluminum-manganese-vanadium orlithium-aluminum-manganese-chromium alloy.
 4. The rechargeable lithiumbattery of claim 1 , wherein said additive is contained in said solventin the amount by volume of 0.1-20%, based on the total volume of thesolvent and additive.
 5. The rechargeable lithium battery of claim 1 ,wherein said solute is lithium trifluoromethane sulfonimide, lithiumpentafluoroethane sulfonimide or lithium trifluoromethane sulfonmethide.6. The rechargeable lithium battery of claim 1 , wherein said solvent isa mixed solvent containing at least one organic solvent selected fromthe group consisting of ethylene carbonate, propylene carbonate,butylene carbonate, vinylene carbonate, γ-butyrolactone and sulfolane,and also containing at least one organic solvent selected from the groupconsisting of 1,2-dimethoxyethane, 1,2-diethoxyethane,1,2-ethoxymethoxyethane, tetrahydrofuran, 1,3-dioxolane, dimethylcarbonate, diethyl carbonate and methyl ethyl carbonate.
 7. Therechargeable lithium battery of claim 1 , wherein said positiveelectrode contains a lithium-manganese complex oxide.
 8. Therechargeable lithium battery of claim 7 , wherein said lithium-manganesecomplex oxide is a complex oxide of lithium and manganese thatincorporates, in the form of solid solution, boron or a boron compound.